1. Field of the Invention
The present invention relates to an imaging sensor and, in particular, to an image device including red, green, and blue color filters and an infrared (IR) pass filter for better color balance.
2. Description of the Related Art
Traditional color imagers, image sensors, and pixelated imaging arrays use a Bayer pattern of pixels and pixel filters, which has a red-green-green-blue (R-G-G-B) pixel/filter configuration (shown in FIG. 1). In such pixelated arrays, the sensor includes individual optical filters that transmit red, green or blue colors and that are disposed at or coated on the individual pixels. Thus, there is a “red pixel” 12a, a “blue pixel” 12b and two “green pixels” 12c arranged to form a 2×2 sub-array 10 that is repeated over the pixelated array.
The three color filters (R, G, and B) not only pass ranges of wavelengths or spectral bands that are corresponding to red, green and blue colors, they also pass through a significant amount of wavelengths in the infrared (IR) or near infrared (NIR) region or band of the spectrum. Therefore, the color imager sensitivity or quantum efficiency spectrum typically has a rich IR or NIR response even with the R, G, and B color pixels. For example, a typical silicon CMOS color sensor's spectrum response is shown in FIG. 2. The spectrum response of the R, G and B pixels (e.g. curves 210, 220 and 230) is comparable or higher than the pixels' response of visible spectrum. The IR light from the environment thus may wash-out the color response in the visible spectrum and may distort the image color reproduction. This is often referred to as IR contamination.
In a traditional color camera, in order to reproduce a true color image, an IR cut-off filter is usually used to cut off or reduce light or energy at or in the IR band or region of the spectrum so as to allow only (or substantially only) the visible light (e.g. light having wavelengths from 390 nm to 700 nm) to pass through the filter so as to be imaged by the RGGB pixels, in order to reduce, limit, or substantially eliminate the IR contamination. Such an IR cut-off filter is typically made of multilayer coatings on a glass or plastic element, such as a flat glass plate, that is added on to a lens assembly of the imager or onto a surface of a lens element of the lens assembly of the imager. The coating process and added material increase the cost of the lens, sometimes significantly